Frontotemporal dementia and neuropsychology: the value of missing values

Objective-To investigate the effect of missing values due to behavioural di sturbances on the neuropsychological test profile in frontotemporal dementi a (FTD). The neuropsychological examination of patients with FTD poses a me thodological problem. in many patients it is impossible to administer a com plete test battery due to behavioural disturbances inherent to the disease. This study describes the test behaviour of patients with FTD, the number o f missing values due to disturbed test behaviour, and its influence on neur opsychological test results. Methods-Thirty one patients with probable FTD were administered a neuropsyc hological test battery including measures of memory, intelligence, and exec utive functioning. Moreover, patients were rated on a global deterioration scale and a test behaviour scale, constructed for this study. Results-The more disturbing the test behaviour, the less tests were assessa ble, leading to many missing values. The most disturbing features were "pos itive symptoms" of FTD, such as perseveration and stimulus boundedness. The effect of test behaviour was largest for tests measuring executive functio ns and reasoning capabilities. The replacement of the missing values due to behavioural disturbances by the lowest score also showed the largest effec t on tests of executive function and reasoning abilities. Conclusion-Data imputation of missing values due to test behaviour disturba nces provides a more differentiated picture of cognitive deficits in FTD.